The present invention relates to the art of a base metal which is coated with a corrosion resistant metal alloy, which corrosion-resistant metal material can be used in a wide variety of applications such as, but not limited to, architectural or building materials such as roofing materials, siding materials, window frames, sheet metal, metal plates and the like; truck and automotive products such as, but not limited to, gasoline tanks, filter casings, body molding, body parts and the like; household products such as, but not limited to, appliance housings, electrical housings, light fixtures and the like; marine products such as, but not limited to, boat hulls, boat masts, dock system components, water retaining systems; and/or other types of metal materials such as, but not limited to, tools, machinery, wires, cables, electrodes, solder and the like. The invention also relates to several novel methods and processes for forming base metals coated with the metal alloy materials, such as but not limited to, coated metal forming by a hot-dip process (i.e plating of metal alloy and subsequent flow heating, immersion in molten metal alloy, metal spraying of metal alloy, and/or roller coating of metal alloy), pretreatment of the base metal prior to metal alloy coating, applying an intermediate barrier metal layer prior to metal alloy coating, post-treating the metal alloy or coated base metal, and/or forming the metal alloy or coated base metal into a variety of different articles.
Over the last several years, there has been a trend in the industry to produce products which are higher in quality, are environmentally friendly, and are safe for use by humans, animals, and/or plants. This push for quality, safety and environmental friendliness is very apparent in the automotive industry wherein both consumer groups and environmental organizations are constantly lobbying for safer, higher-quality vehicles that are more fuel efficient and less detrimental to the environment. Recycling old vehicles has been one answer to resolving the environmental issues associated with vehicles which have run out their useful life. Automotive salvage markets have developed for these vehicles. The vehicles are partially dismantled and sold as scrap metal wherein the metal is melted down and reformed into various parts. Because of the environmentally-un-friendly nature of lead, the gasoline tanks of vehicles must be removed prior to the recycling of the vehicle. Gasoline tanks are commonly made of carbon or stainless steel that are coated with a terne alloy.
Other industries have also demanded higher quality products. These industries include the building industry and marine industry. Corrosion-resistant products that are exposed to various corrosive environments are constantly in demand. Historically, terne coated products were used to coat carbon steel sheets and other carbon steel articles to effectively and inexpensively provide corrosion-resistance to the carbon steel in various applications. Terne or terne alloy is a term commonly used to describe a metal alloy containing about 80% lead and the balance tin. The terne alloy is commonly applied to a the carbon steel by immersing the carbon steel in a molten bath of terne metal by a continuous or batch process.
Although terne coated metals have excellent corrosion-resistant properties and have been used in various applications, terne coated materials have been questioned due to environmental concerns based on the high lead content of the alloy. Environmental and public safety laws have been proposed and/or passed prohibiting or penalizing the user of materials containing a significant portion of lead. As a result, these terne coated articles are typically disposed of in dumping yards or landfills. Not only do these the terne coated articles take up space in the landfills, but there is a concern with the lead leaching from the terne coating into the landfill site and potentially contaminating the surrounding area and underground water reservoirs.
The lead content in terne coated materials is also of some concern for building materials and marine applications. This is especially a concern when the terne coated materials are in contact with drinking water. In many countries, lead pipe has been outlawed to reduce the amount of lead in the water. In many remote locations throughout the world, piped water or well water is not readily available. As a result, structures, such as roof systems, are built to capture rain and to store the rain water for later use. These roof systems supply an important water source for inhabitants utilizing such structures. Roof systems that are designed to collect rain water are typically made of metal to increase the longevity of the roofing system. Typically, the roof systems are made of carbon steel since such metal is less expensive. Terne alloy has historically been used due to its relatively low cost, ease of application, excellent corrosion-resistant properties and desirable colorization during weathering. Roof systems have been made of other metals, but to much less extent due to higher cost and natural corrosion resistance. Such metals include stainless steel, copper, copper alloys and aluminum. Stainless steel, copper, copper alloys and aluminum were typically not coated with a terne coating since these metals have excellent corrosion-resistant properties. However, in some limited applications, these metals have been coated with terne to extend the life of these metals. However, as with lead piping, thereis a concern that the lead in the terne coated roofing materials results in lead dissolving in the collected water.
Terne coated materials have typically been coated with a 6-8 lb. coating (7-11 microns), which is a very thin coating. This thin coating commonly includes pinholes. Terne coated materials that are drawn or formed in various types of materials such as, but not limited to, gasoline tanks, corrugated roofing materials and the like typically included one or more defects in the coating. Due to the thin layer of the terne coating and the pinholes in the coating, the coating on the base metal, upon being drawn by a die or by being formed tended to tear or shear the terne coating and/or elongate the pin holes on the coating thereby exposing the base metal. These exposed surfaces typically corroded at a faster rate than the unexposed surfaces. The corroded regions about the coated areas, in some instances, compromised the adherence of the coated area, thereby resulting, in some instances, to flaking of the coated regions. These corroded regions compromised, in some instances, rapidly compromised the structural integrity, safety and/or performance of the coated base metal. Another disadvantage of using a terne alloy coating is the softness of the terne layer. The softness of the terne coating is susceptible to damage from the abrasive nature of forming machines and to environments that subject the terne coating to frequent contact with other materials.
Terne alloys have a further disadvantage in that the newly applied terne is very shiny and highly reflective. As a result, in some building applications, the highly reflective coating cannot immediately be used. The terne coating eventually loses its highly reflective properties as the components of the terne coating are reduced (weathered); however, the desired amount of reduction commonly takes about 1.5 to 2 years when the terne coating is exposed to the atmosphere. The storage of the terne coated base metal significantly prolongs the weathering of the terne coated materials.
Metallic coatings such as tin or zinc have been tested as substitutes for terne coatings with limited success. The most popular process for applying a tin coating to a base metal is by en electroplating process. In an electroplating process, the coating thickness is very thin and typically ranges between 0.3 microns to 30 microns. The very thin thicknesses of the tin coating typically results in a tin coating having a network of small pinholes, thereby making the coated material generally unacceptable for use in corrosive environments, such as on building materials, marine materials, and automotive products. Such tin plated base metals can include a flash or intermediate metal layer (plated layer) to reduce the pinhole problems inherent with the tin plating process; however, the corrosion effectiveness of the plated tin layer, in some applications, is less than terne coated materials. The tin plated layer is also susceptible to flaking or being scrapped off when the tin plated base metal is drawn through a die and/or formed into various components. The flaking of the tin coating can also cause premature clogging of filter systems and liquid lines, such as in gasoline lines and filters, when the tin plated based metals are formed into gasoline tanks. The pinholes problem, flaking and/or scraping problem that is associated with plated tin coatings is very problematic since tin is not electroprotective under oxidizing conditions. Consequently, discontinuities in the plated tin coating can result in the corrosion of the exposed base metal.
Coating a base metal with zinc metal, commonly known as galvanizing, is another popular metal treatment to inhibit corrosion. Zinc is a desirable metal to coat materials because of its relatively low cost, ease of application, and excellent corrosion resistance. Zinc is also electroprotective under oxidizing conditions and inhibits or prevents the exposed metal, due to discontinuities in the zinc coating, from rapidly corroding. This electrolytic protection extends away from the zinc coating over exposed metal surfaces for a sufficient distance to protect the exposed metal at cut edges, scratches, and other coating discontinuities. Although zinc coatings bond to many types of metals, the bond is typically not very strong thereby resulting in the zinc coating flaking off the base metal over time and/or when being formed. The flaking of zinc, like the flaking of tin coatings, can cause premature clogging of filter systems and liquid lines when zinc coated base metal is formed into gasoline tanks or used in other liquid systems. The flaking of the zinc coating can also result in an undesired and/or disfigured product over a short period of time. Zinc also does not form a uniform and/or thick coating when coating on various types of base metals. Zinc is also a very rigid and brittle metal, thus tends to crack and/or flake off when the zinc coating is formed and/or drawn through a die. When zinc oxidizes, the zinc coating forms a white powdery texture (zinc oxide). This white powdery substance is undesirable for many building applications and in various other environments and applications. One such coating process is disclosed in U.S. Pat. No. 5,399,376, which is incorporated herein by reference. Consequently, the use of a tin coating or a zinc coating as a substitute for terne coatings has not been highly reliable, commercially acceptable or a cost effective substitute for traditional terne coatings. Metal coatings that include a hot dip coating of tin and zinc alloy have been used for fuel tanks as disclosed in Japanese Patent Application No. 47-977776 filed Sep. 29, 1972. The alloy coating thickness was disclosed to be 10-15 microns.
Metal coatings that include electroplated tin and zinc have also been used to coated base metals. Electroplating a tin and zinc mixture onto a steel sheet is disclosed in Japanese Patent Application No. 56-144738 filed Sep. 16, 1981, which is incorporated herein by reference. The Japanese patent application discloses the plating of a steel sheet with a tin and zinc mixture to form a coating thickness of less than 20 microns. The Japanese patent application discloses that after plating, pinholes exist in the coating and subject the coating to corrosion. The pin holes are a result of the crystalline layer of the tin and zinc mixture slowly forming during the plating process. Consequently, the Japanese patent application discloses that the plated tin and zinc coating must be covered with chromate or phosphoric acid to fill the pin holes to prevent corrosion. The Japanese patent application discloses that a preplated layer of nickel, tin or cobalt on the steel sheet surface is needed so that the plated tin and zinc mixture will adhere to the steel sheet.
The coating of steel articles by a batch hot-dip process with a tin, zinc and aluminum mixture is disclosed in U.S. Pat. No. 3,962,501 issued Jun. 8, 1976, which is incorporated herein by reference. The '501 patent discloses that the tin, zinc and aluminum mixture resists oxidation and maintains a metallic luster. The '501 patent discloses that the molten tin and zinc alloy is very susceptible to oxidation resulting in viscous oxides forming on the surface of the molten tin and zinc alloy. These viscous oxides cause severe problems with the coating process. While the steel article is immersed in the molten alloy, a large amount of dross forms on the surface of the molten alloy. The dross results in non-uniformity of the coating and the formation of pin holes as the steel article is removed from the molten metal. The '501 patent discloses that the addition of up to 25% aluminum to the tin and zinc alloy inhibits dross formation, reduces Zn—Fe alloy formation, and reduces viscous oxide formation on the molten bath surface.
The treatment of a steel sheet by plating tin and zinc followed by heat flowing is disclosed in U.S. Pat. No. 4,999,258, which is incorporated herein by reference. The '258 patent discloses a steel sheet plated with a layer of tin and a subsequent layer of zinc. The tin and zinc plated layers are then heated until the zinc alloys with the tin. The tin is applied at 0.2-1.0 g/m2 and the zinc is applied at 0.01-0.3 g/m2. The '258 patent also discloses that when less than 1% zinc is used, the beneficial effect of the zinc is null; however, when more than 30% zinc is used, the coating will rapidly corrode under adverse environments. The '258 patent also discloses that a nickel plated layer is preferably applied to the steel sheet prior to applying the tin and zinc plated layers to improve corrosion resistance. The heat treated tin and zinc layer can be further treated by applying a chromate treatment to the plated layer further improve corrosion resistance.
Due to the various environmental concerns and problems associated with corrosion-resistant coatings applied to base metals and the problems associated with the inadvertent removal of the corrosion-resistant coating during the forming and/or drawing of the coated materials, there has been a demand for a coating or metal material that is corrosion-resistant, is environmentally friendly, and resists damage during forming into end components. Many of these demands where met by the tin alloy or the tin and zinc alloy and process and method for applying these alloys to a base metal which is disclosed in Assignee's U.S. Pat. Nos. 5,314,758; 5,354,624; 5,395,702; 5,395,703; 5,397,652; 5,401,586; 5,429,882; 5,455,122; 5,470,667; 5,480,731; 5,489,490; 5,491,035; 5,491,036; 5,492,772; 5,520,964; 5,597,656; 5,616,424; 5,667,849; 5,695,822; and 6,080,497; and Assignee's U.S. patent application No. Ser. No. 09/634,828 filed Aug. 9, 2000, all of which are incorporated herein by reference.
The use of copper base metals for architectural materials and other applications present unique challenges. Copper is typically more corrosion resistant than carbon steel in many environments. Commercial copper is used for the roofing material and for other types of architectural materials due to its desirable mechanical properties and natural corrosive resistant properties. Copper is one of the strongest pure metals. It is moderately hard, extremely tough, and wear resistant. Though copper in its commercially pure state is very formable thus relatively easily shaped, the copper can be further softened by an annealing process to further improve its formability. Copper alloys can also be used in the architectural materials. Some common alloys of copper are copper-zinc alloys or copper-nickel alloys. Generally, the copper alloys reduce the formability of the architectural materials. Although copper or copper alloy materials have properties that are advantageous in various applications, when copper oxidizes, the oxide forms a black, green or blue-green layer. This color change is unacceptable in a variety of applications. Uncoated copper can also be used to collect water; however, the oxidized copper tends to mix with the water and adversely affects the taste and color of the water. As disclosed in U.S. Pat. No. 5,354,624, copper base materials can be coated with a tin alloy to form a corrosion resistant material that is pliable and that resists formation of a black, green or blue-green layer during oxidation. The life of the copper is significantly extended by coating the copper with the tin alloy.
Due to the various environmental concerns and problems associated with corrosion-resistant coatings applied to copper materials and the problems associated with the forming of the coated copper material into various types of components, there has been a demand for a copper material that is corrosion-resistant, is cost effective to use, is environmentally friendly, resists damage during forming, is pliable, does not oxidize to produce an undesirable color, and is not highly reflective.